The present invention relates to a multicomponent vaccine and methods for preparing a multicomponent vaccine that confers protective immunity to a broad spectrum of infection by Gram negative pathogens. In particular the present invention relates to a multicomponent vaccine that provides both passive and active protective immunity to meningococcal disease.
Meningococcal meningitis is a major problem worldwide and in many countries incidence of infection is increasing. Neisseria meningitidis is the causative agent of the disease and is also responsible for meningococcal septicaemia, which is associated with rapid onset and high mortality, with around 22% of cases proving fatal.
At present, vaccines directed at providing protective immunity against meningococcal disease provide only limited protection because of the many different strains of N. meningitidis. Vaccines based upon the serogroup antigens, the capsular polysaccharides, offer only short lived protection against infection and do not protect against many strains commonly found in North America and Europe. A further drawback of these vaccines is that they provide low levels of protection for children under the age of 2 years, one of the most vulnerable groups that are commonly susceptible to infection.
The meningococcal transferrin receptor is made up of two types of component protein chain, Transferrin binding protein A (TbpA) and TbpB. The receptor complex is believed to be formed from a dimer of TbpA which associates with a single TbpB (Boulton et al. (1998)). Epitopes present in TbpA are known to be masked within the interior of the protein (Ala""Aldeen (1996)). Vaccines against meningococcal meningitis based on TbpB from one strain alone show some cross reactivity and there is evidence of a cross-reactive immune response in rabbits immunised with TbpB alone (Feirrerxc3x3s et al. (1998)).
Gomez et al (Vaccine Vol. 16 (1998) No. 17 pp. 1633-1633) describes a study on the effects of a number of different adjuvant compositions in vaccines comprising TbpA+TbpB complex. Immunization rates against meningococcal challenge were highest in compositions comprising TbpA+TbpB and RAS adjuvant.
Ala""Aldeen (J. Med. Microbiol. Vol. 44 (1996) pp. 237-237 provides a review of Tbps of N. meningitidis and their potential use as candidate vaccine antigens. Ala""Aldeen suggests that cross reactivity and broad spectrum protection is mainly associated with the TbpB subunit (page 240, third paragraph).
Gorringe et al (Vaccine Vol. 13 (1995) No. 13 pp. 1207-1207) describes the human antibody response to Tbps and evaluates their value as vaccine antigens by testing human sera for anti-Tbp antibodies. Gorringe et al does not describe the components of any such vaccine, but investigates the levels of antibody cross reactivity between purified TbpA and TbpB subunits and TbpA+B complex.
Boulton et al (Biochem. J. (1998) 334 pp. 269-273) describes the isolation and characterisation of TbpB from N. meningitidis and also postulates the make-up of the Tbp complex in vivo as a TbpA dimer plus TbpB monomer.
It would be of advantage, nevertheless, to provide a vaccine that gives a broader range of protective immunity to infection from a wider spectrum of strains of N. meningitidis. It would be of further advantage to provide a vaccine that confers protective immunity to infants as well as adults and whose protection is long term. It would also be of advantage to provide a vaccine that protects against sub-clinical infection, i.e. where symptoms of meningococcal infection are not immediately apparent that the infected individual may act as a carrier of the pathogen.
It is an object of the present invention to provide compositions containing Tbps, and vaccines based thereon, that meet or at least ameliorate the disadvantages in the art. In particular, it is an object of the invention to provide a vaccine composition that consistently and reliably induces protective immunity to meningococcal infection.
Accordingly, a first aspect of the present invention provides a composition comprising both transferrin binding proteins A (TbpA) and B (TbpB), suitably in a molar ratio of about 2:1 (TbpA:TbpB). In a preferred embodiment of the present invention the molar ratio of TbpA to TbpB is 2:1.
The composition may be combined with a pharmaceutically acceptable carrierxe2x80x94for example the adjuvant alum although any carrier suitable for oral, intravenous, subcutaneous, intraperitoneal or any other route of administration is suitablexe2x80x94to produce a pharmaceutical composition for treatment of meningococcal disease.
The present invention thus provides for a vaccine comprising both TbpA+B proteins, preferably with a molar ratio of between 1.8 and 2.2 molecules of TbpA to one molecule of TbpB, more preferably 2 molecules of TbpA to one of TbpB. This particular combination of components, surprisingly, can provide higher protective immunity to meningococcal infection, compared to vaccination with TbpB alone. In a specific embodiment of the invention, described in more detail below, a 1:1 combination of A:B is more protective against challenge than B alone. This is surprising as TbpA has previously been considered to be non-protective. The present results differ from this established view with some experiments (described in more detail below) showing that, when administered as a vaccine, TbpA is also able to provide protective immunity to meningococcal infection. However, the present results most strikingly demonstrate the consistent performance of vaccines that comprise both Tbps A and B compared to those comprising Tbp A or B alone. It is this lack of variability between compositions and the consistently high level of protection to infection induced in response to vaccination with Tbp A+B, that enables the compositions of the invention to demonstrate significant advantage over the vaccines of the prior art.
Transferrin binding proteins are known to be located on the outer membranes of a number of Gram negative bacteria such as N. meningitidis. Formulations of the composition of the present invention with conventional carriers or adjuvants provide a composition for treatment of infection by these bacteria.
It is an advantage that following administration of a composition according to the present invention antibodies may be raised against epitopes that consist of sequences from TbpA and TbpB in juxtaposition. Thus, the immune response obtainable using such a composition may be improved compared with that from prior art vaccine compositions which comprise only one component of the Tbp complex and in which the full range of potential Tbp epitopes are unavailable. It is a further option in the present invention for one Tbp subunit component of the TbpA+B complex to be from a first strain of N. meningitidis and another from a second strain different from the first. For example, the TbpA dimer is taken from the first strain and the TbpB is from the second. The TbpA and TbpB proteins may be selected independently from strains K454, H44/76 and B16B6. In all aspects of the invention the Tbps can be directly isolated from the bacterial source or can be produced by recombinant methods commonly known in the art. Combinations of proteins from other strains are also envisaged, and the combining of components from different strains of bacteria offers the potential for providing an individual with a broader spectrum of protection against meningococcal infection. It is further optional for a composition or vaccine of the invention to contain a mixture of A proteins from different strains or a mixture of B proteins from different strains, broadening further the potential spectrum of protection conferred by the invention. A still further option is for Tbps to be obtained from or derived from other bacteria, including N. gonorrhoeae, N. lactamica and Moraxella catarrhalis. 
In the present invention, the term xe2x80x9ctransferrin binding proteinxe2x80x9d or xe2x80x9cTbpxe2x80x9d refers to a protein which either alone binds to transferrin or can be part of a complex of proteins that binds transferrin. The term also embraces fragments, variants and derivatives of such a protein provided that antibodies raised against the fragment, variant or derivative bind the protein. Thus, TbpA and TbpB either dissociated or associated into a complex are considered to be Tbp. Moreover, mutants, fusion proteins or fragments of either TbpA or B or other derivatives of the TbpA+B complex with a common antigenic identity are also considered to be represented by the term Tbp in the present invention.
A second aspect of the invention provides a composition comprising a complex of two TbpAs and one TbpB. The proteins are thus held together in the ratio seen in the native receptor. The individual proteins may be linked, for example, by hydrogen bonds or covalent bonds. In the latter case, each TbpA is covalently linked to the TbpA, either directly or indirectly. In a preferred embodiment, the complex of TbpA and TbpB assumes a native configuration.
A native TbpA+B complex may be isolated and purified from N. meningitidis. Alternatively, the invention also provides for synthesis of recombinant Tbp protein followed by assembly of the TbpA+B complex in vitro. The TbpA+B complex may be formed by admixture, or may be crosslinked by physical (e.g. UV radiation) or chemical methods known to the art, resulting in a combination of Tbps that will remain together and can not dissociate from each other. In a further example, a single chain recombinant protein comprising two TbpA sequences, preferably in the form of the TbpA dimer, is then covalently linked with TbpB protein to form a complete TbpA+B complex in vitro. Another example of the invention in use provides that TbpA and B are mutated so as to introduce cysteine residues that facilitate the formation of disuiphide bridges between the TbpA and TbpB subunits, so as to obtain a covalently bound complex.
In preparation of a recombinant protein TbpA and TbpB genes may also be truncated so that only those domains known to contribute to the antigenicity of the protein are incorporated in the Tbp complex.
In some compositions of the invention the TbpA+B complex is able to act as a transferrin receptor and binds to human transferrin. In other compositions of the invention the TbpA+B complex is non-functional in the sense that it does not bind transferrin, but it nevertheless provides an antigenic component that elicits an appropriate immune response.
A third aspect of the invention provides for a composition comprising a Tbp and N. meningitidis outer membrane vesicles. An advantage of this composition is that when administered to a vaccinee or patient it presents a different combination of N. meningitidis antigens, and particularly antigens that are in a formation substantially as present on the membrane of live infecting organisms. The combination offers the potential for a more effective protection against infection or a broader spectrum of protection than existing vaccines. Known methods of outer membrane vesicle isolation, such as by desoxycholate treatment, are suitable for preparation of compositions of the invention. In various preferred embodiments the Tbp is Tbp A, Tbp B or TbpA+B either in a native complex or in dissociated form.
The outer membrane vesicles may further be pretreated in vitro with Tbp so as to enrich the vesicle membrane with Tbp. By xe2x80x9cenrichxe2x80x9d and like terms, we refer to an outer membrane vesicle to which has been added Tbps so as to increase the concentration or density of Tbps in that vesicle. Preferably, the enrichment results in an outer membrane vesicle having an increased number of transferrin receptors located in the membrane, due to an increased concentration of TbpA and TbpB following their addition to the vesicle and their association into receptors or receptor-like structures. A particular advantage of such embodiments of the invention is that the Tbps, regarded as key antigenic components of the vaccine, are presented in a highly antigenic environment that closely mimics the environment in which transferrin receptors are presented on live, infecting bacteria.
As mentioned previously, the Tbp components of the composition need not be wild-type Tbps. They can be made recombinantly, and in so doing sequence alterations may be introduced. In one typical example of the invention, recombinant TbpB is modified so as to comprise a membrane binding domain. A preferred membrane spanning domain is a hydrophobic alpha helical region added to either the N or C terminus of the Tbp B protein. However, a membrane anchoring region need not only be an alpha helix, addition of a fatty acid or lipid chain would also facilitate membrane anchoring. In fact, wild type TbpB is believed to anchored to the bacterial outer membrane via such a lipid chain anchor. In a further example of the invention in use, the outer membrane vesicles are pretreated in vitro with membrane binding recombinant TbpB so as to enrich the vesicle membrane with TbpB. OMVs enriched with Tbps are additionally generated by inducing high levels of Tbp expression in N. meningitidis and then isolating OMVs via one of the methods described previously. This latter method is typically achieved by transforming the N. meningitidis host with a suitable expression vector into which has been inserted a gene or genes encoding the Tbps of choice. Suitable expression vectors for use in neisserial species include the plasmid pMGC10 (Nassif et al. (1991)).
It is preferred that the composition of the present invention comprises outer membrane vesicles and TbpA+B complexes isolated from a range of different strains of N. meningitidis. Other preferred compositions of the invention comprise other N. meningitidis proteins including surface antigens, periplasmic proteins, superoxide dismutase and glycoproteins.
The composition of the third aspect of the invention may instead of or in addition to outer membrane vesicles comprise one or more liposomes, each liposome including TbpA and/or TbpB preferably including TbpA and TbpB associated into a receptor or into a receptor-like complex. Thus a further means of presenting the transferrin receptor antigens is provided.
In a further embodiment of the third aspect of the invention, the composition comprises 22 kD antigen (Neisserial surface protein A (NspA)) as well as or instead of outer membrane vesicles. NspA and its preparation are described by Martin et al, 1997.
A fourth aspect of the invention provides for a vaccine comprising a composition of the invention as described above. A vaccine of the invention may also comprise antibodies to Tbp and thus provide a level of passive immunity to bacterial infection.
A fifth aspect of the invention provides for a method of manufacturing a composition that comprises combining TbpA, TbpB and N. meningitidis outer membrane vesicles with a pharmaceutically acceptable carrier. It is preferred that the molar ratio of TbpA to TbpB is about 2:1. The outer membrane vesicles can be pretreated in vitro with native TbpA+B so as to enrich the vesicle membrane with Tbp complex. However, the outer membrane vesicles may also be pretreated with other protein components so as to enrich them for these antigenic components also. The outer membrane vesicles may also be pretreated with antigenic proteins and proteoglycans from several different strains of N. meningitidis. 
A further aspect of the invention provides for a composition comprising a Tbp and a Cu,Zn-Superoxide dismutase (Cu,Zn-SOD).
Cu,Zn-Superoxide Dismutase (Cu,Zn-SOD) is an metalloenzyme found in many prokaryotic and eukaryotic organisms. It catalyses the reduction of the superoxide radical anion, O2xe2x88x92, to hydrogen peroxide and molecular oxygen, thus playing an important role in the removal of cytotoxic free radicals from the organism. In bacteria Cu,Zn-SODs have been identified in the periplasm of a number of Gram negative species including N. meningitidis. The enzyme can exist as a dimer or a monomer, and accordingly in a preferred embodiment the present invention provides for a composition comprising a Tbp and a Cu,Zn-SOD of the dimeric type. As mentioned previously with regard to the use of the term xe2x80x9cTbpxe2x80x9d, the Cu,Zn-SOD of the present invention is also considered to encompass fragments, variants and derivatives of such a protein provided that antibodies raised against the fragment, variant or derivative bind the wild type Cu,Zn-SOD.
In examples of the invention in use, compositions are provided that comprise a Cu,Zn-SOD and either a TbpA, a TbpB or a TbpA+B complex. In the latter example it is preferred that the molar ratio of TbpA to Tbp B is between 1.8 and 2.2, with the most suitable compositions having a ratio of 2:1 (TbpA:TbpB). In further compositions of the invention the Tbps are from a different strain of N. meningitidis to that of the Cu,Zn-SOD, thus facilitating the formation of a broader spectrum of immune response to meningococcal infection.
The invention also provides for compositions wherein the Tbps and Cu,Zn-SOD are from different bacterial species, typically different Gram negative species. Such compositions thereby allow an even broader spectrum of immune response to be elicited when administered as a vaccine. Typical compositions comprise a neisserial TbpA+B complex as well as a monomeric Cu,Zn-SODxe2x80x94from E. coli for examplexe2x80x94and optionally a further dimeric Cu,Zn-SODxe2x80x94for example from Haemophilus parainfluenzae. 
Other aspects of the invention provide for methods of manufacturing compositions that provide protective immunity to Gram negative bacterial infection, comprising combining a covalently linked complex of TbpA and TbpB with either or both of N. meningitidis outer membrane vesicles and a Cu,Zn-SOD, plus a pharmaceutically acceptable carrier.
A still further aspect of the invention provides for a composition comprising Tbps and outer membrane vesicles, wherein the outer membrane vesicles are from different strains of N. meningitidis. By analogy, the invention also provides for compositions comprising Tbps and a Cu,Zn-SOD, wherein the Tbps are from different strains of N. meningitidis. 
A further aspect provides for use of Tbps A and B in the manufacture of a medicament for human vaccination. It is preferred that such a medicament is suitable for vaccination against meningococcal infection, although some compositions of the invention provide broad spectrum protection to infection from a wider range of bacterial pathogens.